Embrace the change! Change is a constant reality of software development, a reality that must be reflected in not only our software process but also our software production environment. With ever-changing customer requirements, modifications to the object model are required during software development as well as after product distribution. The associated migration of existing persistent object data is a nontrivial problem. This chapter presents the conceptualization and implementation of a tool for the automated migration of persistent object models. The migration is controlled by an XMI-based description of the difference between the old and the new object model. Both, the schema and the data of the persistent object model are migrated efficiently and reliably.